Mechanical parts such as a gear have to undergo a pitch measurement from the perspective of quality control, because a pitch error in microns may provoke vibration or noise of the machine.
To measure the gear pitch, a contact measurement method that utilizes a probe is primarily employed (for example, refer to Patented Document 1). Noncontact measurement methods include an optical distance measurement method.    [Patented document 1] Japanese Published Unexamined Patent Application No. 2002-107142